Turbochargers may improve engine torque/power output density. A turbocharger may include a compressor and a turbine connected by a drive shaft, where the turbine is coupled to an exhaust manifold side and the compressor is coupled to an intake manifold side. In this way, the exhaust-driven turbine supplies energy to the compressor to increase the pressure in the intake manifold (e.g. boost, or boost pressure) and to increase the flow of air into the engine. The boost may be controlled by adjusting the amount of gas reaching the turbine, for example with a wastegate.
Wastegates may be actuated pneumatically, hydraulically, or electrically. In one example, a wastegate may be actuated via boost pressure produced by the turbocharger. However, it may be advantageous to open the wastegate during low- or no-boost conditions, in order to reduce pumping losses and improve fuel economy. Thus, vacuum-actuated wastegates have been developed to allow for wastegate control during low boost conditions. While vacuum-actuated wastegates may provide robust wastegate control during conditions of high engine vacuum, during higher-boost conditions, the engine intake manifold vacuum used to provide vacuum to actuate the wastegate is not available. A separate vacuum pump may be provided to supply the needed vacuum when engine vacuum is not available, thus wasting fuel.
The inventors have recognized the issues with the above approach and offer a method to at least partly address them. In one embodiment, a method for an engine including a turbocharger having a compressor driven by a turbine comprises generating vacuum via compressor bypass flow through an ejector, and applying vacuum from the ejector to a wastegate actuator.
In this way, the vacuum resulting from a boost condition both acts as a wastegate control signal and is also used to actuate the wastegate. An ejector positioned in the compressor bypass flow may generate vacuum that is directed to the wastegate actuator. Thus, when excess boost is available for vacuum generation via the ejector, the wastegate is opened.
Further, in some examples, vacuum from the intake manifold may also be used to actuate the wastegate, such as when boost pressure is low. By actuating the wastegate with the vacuum-producing ejector during some conditions and with the intake manifold vacuum under other conditions, fully active wastegate control may be provided, thus increasing fuel economy. This is in contrast to previous systems, where in a pressure actuated wastegate, pressure is only available during boosted operation, and in a typical vacuum actuated wastegate, vacuum is only available during non-boosted operation.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.